1. Field of the Invention
The present invention relates to a circuit module in which a component-embedding substrate is used, and more particularly, the present invention relates to a circuit module having a function of an electromagnetic shield, and to a method for manufacturing such circuit modules.
2. Description of the Related Art
In the related art, circuit modules, such as voltage-controlled oscillators (VCOs) and antenna switches, are used in radio apparatuses, such as mobile phones, automobile telephones, and various types of communication apparatuses. A known circuit module has a configuration in which a leakage of an electromagnetic wave generated by a circuit component mounted on a module substrate can be avoided or in which the periphery of the circuit module is covered by shielding electrodes in order to block an electromagnetic wave that enters the circuit module from the outside.
FIG. 12 shows an example of a circuit module having a function of an electromagnetic shield. On the surface of a wiring substrate 60, a ground electrode 61 and an input-output electrode 62 are provided, and, on the back surface of the wiring substrate 60, terminal electrodes 63 are provided. In the wiring substrate 60, inner via-holes 64 and internal wiring patterns 65 are provided. A circuit component 66 is bonded to the ground electrode 61 and the input-output electrode 62 using a conductive bonding material 67, such as solder or a conductive adhesive. Subsequently, the top of the wiring substrate 60 is covered by an insulating resin layer 68 such that the circuit component 66 is disposed in the insulating resin layer 68, and the external surface of the insulating resin layer 68 and the peripheral surfaces of the wiring substrate 60 are covered by electromagnetically shielding layers 69.
In order to manufacture the circuit module with outstanding productivity, the wiring substrate 60, which is an aggregate substrate, is prepared, and the circuit component 66 is mounted on the wiring substrate 60. Then, the wiring substrate 60 and the circuit component 66 are sealed with the insulating resin layer 68, and divided into small substrates. Subsequently, the electromagnetically shielding layers 69 are provided. On the top surface of the insulating resin layer 68, one of the electromagnetically shielding layers 69 can be formed in the aggregate substrate state. However, on the side surfaces of the insulating resin layer 68 and the wiring substrate 60, the electromagnetically shielding layers 69 must be formed after the division into small substrates. Consequently, this leads to a problem that the productivity is decreased, and inconsistent quality often occurs.
In Japanese Unexamined Patent Application Publication No. 2005-159227, a circuit module in which shielding layers are provided so as to cover the surfaces surrounding a surface that a component is mounted on and the productivity of which is excellent is provided.
FIGS. 13A to 13G show an example of a manufacturing process of the circuit module disclosed in Japanese Unexamined Patent Application Publication No. 2005-159227. The process includes the steps of preparing a multi-layered wiring substrate 70 that is an aggregate substrate (FIG. 13A), printing solder or a conductive adhesive 71 on the wiring substrate 70 (FIG. 13B), mounting a circuit component 72 (FIG. 13C), forming an insulating resin layer 73 (FIG. 13D), forming a shielding layer 74 on the top surface, and then, curing the insulating resin layer 73 by heat treatment (FIG. 13E), providing cutting grooves 76 in the insulating resin layer 73 at boundary portions between adjacent small substrates such that ground electrodes 75, which are formed on the wiring substrate 70, are exposed (FIG. 13F), filling and performing heat-curing of a conductive material 77 in the cutting grooves 76 (FIG. 13G), and cutting the conductive material 77 along the cutting grooves 76 using a blade having a width less than that of the cutting grooves 76, so to be divided into pieces.
However, in the circuit module having the above-described configuration, the depth of the cutting grooves, which are to be filled with the conductive material defining a shield, extends only to a plane providing an exposure of the ground electrode, which is formed on the surface of the wiring substrate. The depth of the cutting grooves can be set such that the cutting grooves extend into the wiring substrate 70. However, in order to ensure the mechanical strength of the aggregate substrate when being filled with the conductive material, it is difficult to provide cutting grooves having a very large depth. For this reason, it is difficult to use a wiring substrate having a very small thickness, and this causes the side surfaces of the wiring substrate to have portions on which no shielding layer is formed. Thus, a problem occurs in that it is difficult to obtain a sufficient shielding property.
As in Japanese Unexamined Patent Application Publication No. 2005-159227, it is not easy to precisely equalize the depth of cutting grooves to a depth corresponding to a height providing an exposure of ground electrodes formed on the surface of a wiring substrate. There is a probability that the ground electrodes may be damaged or cut. This causes the decrease in productivity.